Dynamic intervertebral spacer implant

Abstract

Intervertebral spacer implants with dynamic load spreading features responsive to external loads and having attachment mechanisms. The dynamic load spreading features having a native state and a loaded state, which complements vertebral end plate geometry and disperses load to the epiphyseal rim.

Description

TECHNICAL FIELD[0001]The present invention relates to intervertebral spacer implants. More specifically, the present invention relates to spinal interbody fusion implants (spacers) having dynamic elements on at least one side of the implant body. Implants with dynamic or flexible elements allow the spreading of intervertebral load across the end plate of the vertebral body. Increasing the contact area from a point to a large surface and particularly loading the vertebral body toward the outer rim, where the bone density is generally higher, reduces implant subsidence. Additionally, maintaining several points of contact across the end plate reduces implant movement. Lastly, having dynamic elements reduces the overall stiffness of the spacer and allows the bone graft material packed within it to carry part of the load that is being transferred from one adjacent vertebral body to the vertebral body on the opposite side of the spacer. This disclosure is made in the context of interverte...

AI Technical Summary

Benefits of technology

The present invention provides systems and methods that can address the problems of current implants in the market. These systems can make it easier to prepare for surgery, reduce the likelihood of the implant moving around or becoming dislodged, support bone growth, and make it easier to see the bone on x-ray images.

Problems solved by technology

Lastly, having dynamic elements reduces the overall stiffness of the spacer and allows the bone graft material packed within it to carry part of the load that is being transferred from one adjacent vertebral body to the vertebral body on the opposite side of the spacer.

Intervertebral disc pathology can result in the absence of physiological loading of vertebral end plates resulting in instability or degenerative changes over time, which may lead to spinal stenosis and neurological complications.

The seating of threaded cylindrical implants may also compromise biomechanical integrity by reducing the area in which to distribute mechanical forces, thus increasing the apparent stress experienced by both the implant and vertebrae.

Further, a substantial uncontrolled risk of implant subsidence (defined as sinking or settling) into the softer cancellous bone of the vertebral body may arise from such improper seating.

Even open ring-shaped cage or spacer implant systems, generally shaped to mimic the anatomical contour of the vertebral body, lack the ability to complement specific stiffness of the patient's bone.

Such allograft bone material restricts the usable size and shape of the resultant implant.

Therefore, these allograft cages may not be of a sufficient size to contact the strong cortical bone, the uncinate process, or apophyseal rim of the vertebral endplate.

These size-limited implant systems may also poorly accommodate related instrumentation such as drivers, reamers, distractors, and the like.

For example, these implant systems may lack sufficient structural integrity to withstand repeated impact and may fracture during implantation.

Further, other traditional non-allograft ring-shaped cage systems may be size-limited due to various and complex supplemental implant instrumentation, which may obstruct the disc space while requiring greater exposure of the operative field.

These supplemental implant instrumentation systems also generally increase the instrument load on the surgeon.

Traditional interbody spinal implants generally do not seat properly on the preferred structural bone located near the apophyseal rim of the vertebral body, which is primarily composed of preferred dense subchondral bone.

In the process of aggressive end-plate removal, however, the end-plates are typically destroyed.

Such destruction means that the load-bearing implant is pressed against soft cancellous bone increasing the risk of implant subsidence.

The end-plates are concave; hence, if a flat implant is used, the interface will not be well matched and the implant may not be very stable.

Even if a convex implant is used, it is very difficult to match the implant geometry with the end-plate geometry, as the end-plate geometry varies from patient-to-patient and on the extent of disease.

This method also violates the structure.

Both options can create localized stress risers in the end-plates, increasing the chances of subsidence.

The challenge of preventing implant expulsion is especially acute for PEEK implants, because the surface texture of PEEK is co very smooth and slippery, with reduced purchase on the adjacent vertebrae.

Subsidence of the implant is a complex issue and has been attributed to many factors.

These design restrictions do not leave much room for filling the bone graft material into cortical bone implants.

The exposure-driven limitations on implant size narrow the room left inside the implant geometry for bone grafting even for metal implants.

In many cases, the typical interbody fusion implant is not able to incorporate with the vertebral bone, even years after implantation.

Such inability persists despite the use of a variety of different materials to construct the implants.

Stiff, typically metallic, implants stress shield the bone graft and do not supports its transformation into living bone.

For implants made of metal, the metal limits adequate radiographic visualization of the bone graft.

Hence it can be difficult to assess fusion, if it is intended to take place.

Metal implants are dense and inhibit the assessment of boney fusion via x-ray techniques.

In addition, they can create significant artifacts when utilizing MRI or CT scans to post-operatively visualize the implant / bone interfaces.

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